Most organic materials do not preserve over tens of thousands of years under most conditions.

The specific combination of dental tissue (which preserves very well) and arecoline chemical traces (which apparently survive in that dental tissue over geological timescales under the right conditions) is unusual.

Before the Sulawesi discovery, no one had specifically looked for arecoline in ancient dental tissue from the Ice Age because no one had reason to think that betel nut use went back that far.

The distinctive dental wear pattern was the clue that prompted the chemical analysis.